1. Field of the Invention
The present invention relates to the general field of electrical connectors and is particularly concerned with a submersible, set-screw type, electrical connector.
2. Description of the Related Art
Electrical distribution systems are used extensively in most industrialized countries. These distribution systems typically include power cables, transformers and connectors for linking the components together. Some distribution systems are designed with the intent of having cables suspended from poles anchored into the ground so that the cables are located substantially above the ground surface. In such instances, the transformers and connectors are also mounted on the poles above the ground surface. Other, often more recent electrical distribution systems are designed so that the cables, transformers and connectors are located under the ground surface or in electrical pedestals. In such instances, the connections are usually made below grade in an access hole, or aperture, or in a vault, all being characterized by relatively confined space.
Many power cables have been and are being manufactured with segmented or non-segmented center conductors formed from aluminum wire strands rather than copper wire strands due to the availability of the aluminum wire and its usually lower cost. The use of aluminum wire strands, however, has its disadvantages or drawbacks.
One major drawback of aluminum wire strands is the rather rapid formation of aluminum oxide coatings on the outer surfaces of the aluminum wire strands and of associated aluminum connecting devices. Such coatings retard the flow of electrical current across the junction formed by the aluminum wire strand and a connecting device.
Additionally, aluminum wire strands experience relatively rapid metal fatigue when subjected to temperature and contraction cycles caused by changes in the ambient temperature and the operational temperature of the electrical system.
Many different types of connectors are used in the prior art to electrically couple or connect the center conductor of a low voltage distribution network to an external electrical connector. A particularly popular type of electrical connector is the so called set-screw electrical connector. These connectors typically include bodies of aluminum or copper/aluminum alloy typically having a generally parallelepiped-shaped configuration. The connector bodies are conventionally made out of an extrusion or by another suitable manufacturing process.
The parallelepiped-shaped configuration or other suitable configuration defines a first surface divided with conductor receiving blind holes or channels. A second surface typically oriented in a generally perpendicular relationship relative to the first is provided with corresponding and intersecting blind tapped holes or channels. These latter channels are configured, sized and positioned for receiving so called set-screws usually having hexagonal heads.
In use, the conductors are inserted into a blind conductor receiving hole when the set-screw is backed off. The set-screw is then tightened down on the conductor to clamp it to the body and to make the connection. Typically, the number of connections may be in the order of one to eight or even more. Such connectors are commonly used with secondary pad mount transformers, utility pedestals or the like. Examples of such structures include underground extruded or cast connectors, splices, and overhead connectors such as metering and grounding lugs.
When the connectors are used in underground distribution systems, the connections are typically made in a wet environment. It is also possible that the connection could be submerged at some point over its service life due to environmental factors such as rain, floods or even normal seasonal fluctuations of ground water. cables by the set-screws, and required for maintaining the cables within the conductor channels formed in the connectors, is such that it typically tends to spread the individual cable wires apart further reducing the effective contact area.
The poor contact problem is further compounded by the fact that the connectors are often subjected to temperature cycling which leads to cold flow, hence reducing electrical efficiency and reduced contact surfaces.
Another drawback associated with conventional set-screw type connectors, especially of the submersible type, is that although some are provided with encasing coatings, their design is such that some metallic part is often in contact with the external environment during installation and/or uninstallation procedures. Consequently, operators performing the connection or service must resort to using cumbersome, unergonomical and time consuming safety equipment.
Still further disadvantages associated with prior art set-screw type connectors relates to their relatively unergonomical design requiring manual dexterity on behalf of the operator who needs to perform size movements in a generally confined space in a difficult environment.
Upper insertion of the conductor cable in the corresponding cable receiving channel and manipulation of the protective caps mounted over the screw heads are but a few examples of numerous difficult tasks that must be performed with care due to the inherent unergonomical design of the prior art set-screw type connectors.
Accordingly, there exists a need for an improved electrical set screw type connector.
It is therefore the purpose of the present invention to provide an improved electrical set-screw type connector that will circumvent at least some of the drawbacks associated with prior art connectors. More particularly it is the purpose of the present invention to provide an improved electrical set-screw type connector that provides better contact between the conductors and the block thereby making it more efficient. It is another object of the present invention to provide an improved connector that is waterproof and that has no exposed metal parts making it safer and more reliable in use. It is another purpose of the present invention to provide an improved connector that is easier to use when making or changing connections.
In accordance with the present invention there is provided an electrical connector with an elongated, metallic, adapter located between the exposed conductor in each conductor channel and the associated set-screw in the connector block. When the set screw is tightened, it pushes the adapter against the conductor spreading the pressure exerted by the set-screw over the length of the exposed conductor and pushing it more evenly against the block over its length so as to provide better contact and thus improve efficiency. In addition, the use of the adapter helps maintain cable integrity and minimizes spreading apart of the strands of the conductor. Preferably, a belleville washer can be inserted between each set-screw and its associated adapter, the washer helping to maintain a constant pressure on the conductor by minimizing the effect of temperature related expansion/contraction cycles. The invention is also directed toward a connector block constructed to receive an adapter in each conductor channel.
In a preferred embodiment of the invention, the connector is encased in insulting material such as rubber. The rubber casing provides inlets to the conductor channels for the channels to receive the conductors and provides inlets to the set-screw channels for the channels to receive the set-screws. Both inlets are designed to be sealed against water. The inlets to the channels for the conductors are provided with closure caps having an elastic end wall with an expandable opening therein through which the conductor is passed. The elastic opening makes it easier to connect the conductors to the block and also makes it simpler to use different sized conductors in the same block. The inlets to the channels for the set-screws are dimensioned to snugly receive the set-screws preventing the entry of water. The set-screws are preferably made of non-conducting material such as plastic. No metal parts are thus exposed when the connector is encased.
Advantages of the present invention include the proposed set-screw connector allowing improved connective efficiency of a conventional electrical power cable. The proposed set-screw connector is designed to improve conductor contact so as to reduce the resistivity of the connection and, hence, reduce the heat generated thereby improving the conductivity and over all efficiency.
Furthermore, the proposed set-screw type connector is designed for receiving and retaining the center conductors of various sizes of power cables without requiring expensive and/or cumbersome modifications. The proposed set-screw type connector is designed so as to facilitate connection of the conductor cables without requiring special tooling or manual dexterity through a set of ergonomical, easy and efficient steps. Also the design facilitates insertion of the conductor cables and eases the application of the set-screws, at least in part by eliminating the need for screw caps.
Also, the proposed connector design allows for improved characteristics over an extended period of time. It also allows for improved insulation against water contact and provides a structure exempt of exposed metallic surfaces which in turn, reduces the need for expensive and cumbersome protection equipment.
Still further, the proposed set-screw type connector is designed with a reduced number of components compared to most prior art connectors and is also designed as be relative compact, again facilitating use thereof in relatively confined areas. Still further, the proposed connector is designed so as to be manufacturable using conventional forms of manufacturing so as to provide a connector that will be economically feasible, long lasting and relatively trouble free in operation.
The invention is particularly directed toward a block made of electrically conductive material, the block forming part of a set-screw type electrical connector. The block has a first surface with at least one conductor channel extending into the body from the first surface and a second surface with at least one set-screw channel extending into the block from the second surface. There is at least one set-screw channel associated with each conductor channel. Each set-screw channel intersects its associated conductor channel. Each conductor channel has a conductor receiving section and an adapter receiving section, both sections extending substantially the length of the channel. The adapter receiving section is located between the conductor receiving section and the associated set-screw channel.
The invention is also particularly directed toward a set-screw type electrical connector having a block made of electrically conductive material. The block has a first surface with at least one conductor channel extending into the body from the first surface and a second surface with at least one set-screw channel extending into the block from the second surface, there being at least one set-screw channel associated with each conductor channel. Each set-screw channel intersects its associated conductor channel. Each conductor channel has a conductor receiving section and an adapter receiving section, both sections extending substantially the length of the channel. The adapter receiving section is located between the conductor receiving section and the associated set-screw channel. An elongate adapter is provided for each conductor channel, the adapter sized and shaped to fit in the adapter receiving section in the conductor channel. A set-screw is threadable into each set-screw channel to contact the adapter in each conductor channel associated with each set-screw channel, and to press the adapter tightly against a conductor inserted in the conductor receiving section of the conductor channel.